North Korea obtains significant funding for its ballistic missile and nuclear weapons programs from exports of slave labor overseas.

The authorities in a northeastern Chinese border city have secretly warned local firms they will be slapped with fines if they newly hire North Korean workers in violation of United Nations sanctions, amounting to 5,000 yuan ($750) per worker, sources familiar with the situation said Wednesday.

The report states that seafood from the Hunchun plants was sold to Walmart and also under the Sea Queen brand, which is sold exclusively at Aldi supermarkets. These same laborers also work in factories that make wood flooring and clothes in Hunchun, a Chinese city near the North Korean and Russian borders. And they are paid a fraction of their salaries, while the rest-as much as 70 percent-is taken by North Korea's government.

"While we understand that hiring North Korean workers may be legal in China", he said, "we are deeply concerned that any seafood companies could be inadvertently propping up the despotic regime". The United States now considers all forms of North Korean labor slave labor. The jobs, which are highly sought after by North Korean citizens, can generate an estimated $200 to $500 million a year for the regime.

Securing North Korea's missile launchers and nuclear, chemical and biological weapons sites would likely be a chief priority for China in the event of a major crisis involving its communist neighbour, analysts say, although Beijing so far is keeping mum on any plans.

John Connelly, president of the National Fisheries Institute, the largest seafood trade association in the United States, told AP his group was urging all of its companies to immediately re-examine their supply chains "to ensure that wages go to the workers, and are not siphoned off to support a risky dictator".

What's less clear is whether and under what conditions China would commit troops as an occupying force should North Korean leader Kim Jong Un's regime fall apart, Mr. Cheng said.

"It is unbelievable that they would be going home in bright outfits with these smiles on their faces", RFA's source said, speaking on condition of anonymity.

Seafood can remain in the supply chain for more than a year. There's no way to say where a particular package ends up, nor what percentage of a factory's products wind up in the U.S.

A worker stacks crates at the Yanbian Shenghai company which hires some North Korean workers to process seafood in Hunchun. Thai Union said the sister company they do business with meets all of their fair labor standards, and should not be penalized just because they have the same owner.